The invention relates to a compound selected from one or more of the following: a tris (hydroxymethyl) methylamine salt of (2S)-2-ethoxy-3-(4-{2-[hexyl (2-phenylethyl) amino]-2-oxoethoxy}phenyl) propanoic acid; an ethanol amine salt of (2S)-2-ethoxy-3-(4-{2-[hexyl (2-phenylethyl) amino]-2-oxoethoxy}phenyl) propanoic acid; or a pharmaeutical composition comprising the compound.